Microwave coupled line device having insulated coupled inner conductors within a common outer conductor



Dec. 12, 1967 T. s. SAAD 3,358,248

MICROWAVE COUPLED LINE, DEVICE HAVING INSULATED COUPLED INNER CONDUCTORSWITHIN A COMMON OUTER CONDUCTOR Filed July 22, 1964 //VVEN7U/?.'THEODORE S. SAAD ATTORNEYS United States Patent 3,358,248 MICROWAVECOUPLED LINE DEVICE HAVING INSULATED COUPLED INNER CONDUCTORS WITHIN ACOMMON OUTER CONDUCTGR Theodore S. Saad, Westwood, Mass., assignor toSage Laboratories, Inc, East Natick, Mass., a corporation ofMassachusetts Filed July 22, 1964, Ser. No. 334,455 3 Claims. (Cl. 333-)ABSTRACT OF THE DISCLOSURE A microwave coupled line device includes apair of insulated inner conductors, each having inulation bonded theretoand separated by the thickness of the insulation therebetween for adistance corresponding substantially to a quarter wavelength at thecenter operating frequency, the thickness of the insulation beingcomparable to and typically less than the thickness of each conductor. Acommon outer conductor surrounds and is insulatedly separated by anannular bead from the inner conductors by a radial distance greater thanthe radial distance spanned by the assembly of the inner conductors andthe insulation therebetween and many times greater than the thickness ofthe insulation therebetween. In a specific form, there are four terminalpairs outside the cavity enclosed by the outer conductor with eachterminal pair having its inner terminal coupled to a respective end ofthe inner conductors and its outer terminal intercoupled with the otherouter terminals by the common outer conductor.

The present invention relates in general to coupled line devices andmore particularly concerns a novel hybrid of high electricalperformance, small physical form and easy and inexpensive to fabricatein large and small quantities while maintaining a high degree ofrepeatability in electrical performance and facilitating the convenientlocation of external terminals.

One well known type of four terminal pair hybrid comprises a pair ofconductors centered in an outer conductor with precision supports thatmaintain quarter-wavelength segments of the two conductors in precisefixed relationship. Each end of the two conductors is brought out to theinner terminal of a coaxial terminal pair so that when the terminalpairs are properly terminated, energy applied to one terminal pairdivides equally and in phase quadrature to the nearest two terminalpairs while substantially no energy is delivered to the farthestterminal pair. While these hybrids perform satisfactorily, precisemachining and assembling procedures are required to achieve satisfactorylevel of performance. Moreover, relatively large conductors have beenemployed with the result that the size of these hybrids is notinfrequently greater than that desired. Moreover, relatively large sizedconductors react with a surrounding outer conductor so as to alter theelectrical properties and frequently require the introduction of specialcompensating elements within the cavity. And the geometry of thespecific structure frequently limits the available locations for outputterminals.

Accordingly, it is an important object of this invention to provide ahigh performance miniaturized coupled line device that is relativelyeasy and inexpensive to fabricate.

It is another object of the invention to provide a hybrid in accordancewith the preceding object that facilitates convenient location ofterminals for connection to external apparatus.

According to the invention, first and second inner conductors withinsulation bonded thereto are arranged within an insulatedly separatedouter conductor side-by-side for a quarter wavelength, separated by theinsulation thickness therebetween. The ends of the inner conductors arecoupled to a respective signal terminal of a terminal pair, the otherterminal of each pair being a reference terminal intercoupled by theouter conductor with the other reference terminals.

Numerous other features, objects and advantages of the invention willbecome apparent from the following specification when read in connectionwith the accompanying drawing in which:

FIG. 1 is a longitudinal sectional view, and

HG. 2 is a central diametrical sectional view of an embodiment of thisinvention comprising two insulated Wires contiguous for a quarterwavelength in a circular cylinder.

With reference now to the drawing and more particularly FIG. 1 thereof,there is shown a longitudinal sectional view of the embodiment of theinvention in which the four terminal pairs A, B, C and D of the hybridare diagrammatically represented. When these terminal pairs areterminated in their respective characteristic impedances, energy appliedto one terminal pair divides equally between the nearest two terminalpairs While negligible energy is delivered to the farthest terminalpair. Thus, energy applied to terminal pair A divides equally betweenterminal pairs B and C in phase quadrature while virtually no energy isdelivered to terminal pair D. Conductor 11 intercouples signal terminal12 of terminal pair A and signal terminal 13 of terminal pair C.Conductor 13 intercouples signal terminal 14 of terminal pair B andsignal terminal 15 of terminal pair D. Thin layers of insulation 16 and17 are bonded to conductors 11 and 13, respectively. These insulatingportions are in contact along the line 21 for a quarter wavelength atcenter frequency so that the conductors 11 and 13 are separated by theinsulation thicknesses. An annular insulating Wafer 22 supports theinsulated conductors 11 and 13 symmetrically within the conductingcylindrical casing 23 defining the outer conductor. Casing 23 alsointercoupled the interference terminals 24, 25, 26 and 27 of terminalpairs A, B, C and D, respectively.

FIG. 2 is a diametrical sectional view through the embodiment of FIG. 1illustrating how the insulating wafer 22 keeps conductors 11 and 13centered within the cavity defined by the conductive casing 23.

In a specific embodiment of the invention No. 20 wire with a Tefloncoating .004 inch thick was placed in a cylindrical cavity 1.460 incheslong, .234 inch in diameter, and the ends of each wire brought out totype TNC coaxial terminals to provide a coupling of 3 db 0.4 db and anisolation of 29 db minimum over a frequency range of l to 2 gigacycles.The annular supporting head was made of Teflon and had an inner diameterof .067 inch.

An important feature of the invention is the adaptability of thestructure to accommodating terminal pairs at different locations. FIG. 1shows terminal pairs being brought out at diametrically opposed pointsin the cylindrical outer conductor. But the invention operates equallywell with the terminal pairs in space quadrature. Alternatively,terminal pairs could be brought out through the end caps of the cavity.Also, the wires can be internally twisted up to without affectingperformance.

The invention is illustrated with separate circular wires in a circularcavity. The cavity could be rectangular or of other shape. The wirescould be rectangular and might be bonded to a common separatinginsulating strip.

Other modifications and uses of and departures from the specificembodiments described herein may be practiced by those skilled in theart without departing from the inventive concepts. Consequently, theinvention is to be construed as limited solely by the spirit and scopeof the appended claims.

What is claimed is:

1. High frequency apparatus operative over a frequency range embracing apredetermined center frequency comprising,

first and second insulated inner conductors, each having insulationbonded thereto and separated by the thickness of said insulationtherebetween for a distance corresponding substantially to a quarterwavelength at said center frequency and separated by a greater distance.elsewhere,

the thicknes of said separating insulation being less than the thicknessof each conductor,

means including an outer conductor defining a cavity surrounding andinsulateally separated from said inner conductors and maintained infixed relationship, with the radial distance between said outerconductor and said inner conductors being greater than the combinedthickness of said inner conductors with said separating insulation andbeing many times greater than the distance between said innerconductors, established by said separating insulation,

means defining four terminal pairs outside said cavity,

each terminal pair having a signal terminal coupled to a respective endof said conductors and a reference terminal intercoupled with the otherreference terminals by said outer conductor.

2. High frequency apparatus in accordance with claim 1 and furthercomprising,

means for supporting said first and second inner conductors symmetricalabout the axis of said outer conductor for at least said quarterwavelength, said inner conductors being much closer to said axis than tosaid outer conductor along said quarter wavelength. 3. High frequencyapparatus in accordance with claim 2 wherein said inner conductors andsaid outer conductor are of substantially circular cross section andsaid means for maintaining comprises an insulating annular bead of innerdiameter corresponding substantially to the radial distance spanned bysaid first and second'insulated inner conductors, of outer diametercorresponding substantially to the inner diameter of said outerconductor and of length corresponding substantially to said commonlength and snugly surrounds said first and second insulated innerconductors.

References Cited UNITED STATES PATENTS 2,679,632 5/1954 Bellows 333-103,105,207 9/1963 Ca pewell et al. 333 10 3,237,130 2/1966 COhn 333 10FOREIGN PATENTS 1,197,584 12/1959 France.

1,146,559 4/1963 Germany.

HERMAN KARL SAALBACH, Primary Examiner.

RONALD D. COHN, SAXFIELD CHATMON, 1a., Assistant Examiners.

1. HIGH FREQUENCY APPARATUS OPERATIVE OVER A FREQUENCY RANGE EMBRACING A PREDETERMINED CENTER FREQUENCY COMPRISING, FIRST AND SECOND INSULATED INNER CONDUCTORS, EACH HAVING INSULATION BONDED THERETO AND SEPARATED BY THE THICKNESS OF SAID INSULATION THEREBETWEEN FOR A DISTANCE CORRESPONDING SUBSTANTIALLY TO A QUARTER WAVELENGTH AT SAID CENTER FREQUENCY AND SEPARATED BY A GREATER DISTANCE ELSEWHERE, THE THICKNESS OF SAID SEPARATING INSULATION BEING LESS THAN THE THICKNESS OF EACH CONDUCTOR, MEANS INCLUDING AN OUTER CONDUCTOR DEFINING A CAVITY SURROUNDING AND INSULATEDLY SEPARATED FROM SAID INNER CONDUCTORS AND MAINTAINED IN FIXED RELATIONSHIP, WITH THE RADIAL DISTANCE BETWEEN SAID OUTER CONDUCTOR AND SAID INNER CONDUCTORS BEING GREATER THAN THE COMBINED THICKNESS OF SAID INNER CONDUCTORS WITH SAID SEPARATING INSULATION AND BEING MANY TIMES GREATER THAN THE DISTANCE BETWEEN SAID INNER CONDUCTORS, ESTABLISHED BY SAID SEPARATING INSULATION, MEANS DEFINING FOUR TERMINALS PAIRS OUTSIDE SAID CAVITY, EACH TERMINAL PAIR HAVING A SIGNAL TERMINAL COUPLED TO A RESPECTIVE END OF SAID CONDUCTORS AND A REFERENCE TERMINAL INTERCOUPLED WITH THE OTHER REFERENCE TERMINALS BY SAID OUTER CONDUCTOR. 